Known pressure switches include a housing having a cavity for receiving a fluid under pressure. A pressure-transducing element is in fluid communication with the cavity and is utilized to measure the pressure of the fluid. The cavity extends from an inlet to an outlet of the pressure switch and defines a flow path for the fluid. The pressure-transducing element is disposed in the flow path between the inlet and the outlet.
Pressure switches of this type are known from, e.g., DE 19 57 687 A, JP 08-304197 A and DE 101 55 839 A1 (US 2002-0059833). They are utilized, e.g., in lubrication systems that supply grease to machine components. In such applications, the grease must be maintained at a certain pressure. If the pressure drops, more grease must be pumped by a grease pump. Accordingly, a pressure switch of the above-mentioned type monitors the pressure of the grease (lubricant), which is disposed in a defined portion of the system, in real time.
Known pressure switches typically have a blind end (dead space) in the connector before the pressure chamber. The grease does not circulate in the blind end (dead space) and consequently it is not flushed out (replaced) during operating. Therefore, the grease located there can age and the aging is accelerated by the alternating pressure. As a result, the grease may separate over the time (i.e. the base oil “bleeds out”) and harden.
The designs of the above-noted pressure switch necessitate such a dead space (blind end), which may be even further enlarged by inserting T-pieces in the vicinity of other connection fittings.
The above-mentioned grease hardening effect is strongly dependent on the specific bleeding behavior of the grease, as well as its flow properties and its solid content. However, appropriate selection of the grease for the particular system can minimize this problem only to a limited extent.
Therefore, in previously known pressure switches of the above-mentioned type, a grease plug can form and harden to such a degree that the pressure switch does not function any more, i.e. it no longer switches in accordance with its rated pressure threshold(s).